Such a device is known from the article "A Planar Indium Phosphate Monomode Waveguide Evanescent Field Immunosensor" by A. N. Sloper, J. K. Deacon and M. T. Flanagan, in Sensors and Actuators, B1 (1990), pp. 589-591.
This article particularly refers to a first embodiment in which a thin-film waveguide is provided on a glass substrate. By means of a device for coupling in excitation light, which is fixed relative to the thin-film waveguide, monochromatic laser light is coupled into the thin-film waveguide in such a way that it is conducted through the thin-film waveguide parallel to the surface thereof. The fluorescent dye which is contained in a sample applied to the thin-film waveguide is excited by the evanescent field of the laser light propagating along the thin-film waveguide. The fluorescent light emitted by the fluorescent dye is finally detected by a photomultiplier means.
The article further reveals a second embodiment of the above-described device, in which the device for exciting the fluorescent dye to be detected is provided in the form of a glass plate with a device for coupling in excitation light, monochromatic laser light from a light source which is fixed relative to the glass plate being coupled into said glass plate by said excitation light coupling device in such a way that it is conducted through said glass plate at an angle of total reflectance.
Just as in the case of the thin-film waveguide, a fluorescent dye contained in a sample applied to the glass plate is excited by the evanescent field of the laser light also in the case of this embodiment. The fluorescent light resulting from this excitation is then again detected by a photomultiplier means.
A disadvantage of both embodiments known from the prior art is, however, that these embodiments are very difficult to handle in practical applications, i.e. when a plurality of samples is to be analyzed. In particular, the thin-film waveguide and the glass plate, respectively, must be cleaned after each analysis of a sample, whereupon a new sample has to be applied and the thin-film waveguide or the glass plate with the sample applied thereto has to be adjusted with respect to the light source and the detecting means. An analysis of a plurality of samples by means of the device known from the prior art is therefore very time-consuming.